JP2002188061A - Double-sided tacky sheet excellent in impact resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided tacky sheet excellent in impact resistance, scarcely causing dropping of parts by shock when an electronic equipment fixed with the double-sided tacky sheet is dropped. SOLUTION: This invention provides the double-sided tacky sheet in which a tacky agent layer of at least one side of the double-sided tacky sheet has a maximum value of loss tangent in a frequency zone of maximum natural frequency or above in vibration generated when an electronic equipment is dropped and has >=1 maximum of the loss tangent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact-resistant double-sided pressure-sensitive adhesive sheet for fixing components of electronic equipment.

[0002]

2. Description of the Related Art Double-sided pressure-sensitive adhesive sheets are used for fixing parts in various industrial fields because of their good workability and workability. In particular, it is more advantageous than the adhesive when the part to be fixed has a complicated shape or when productivity in an automated line is required. Therefore, a double-sided pressure-sensitive adhesive sheet is used for fixing a nameplate of an electronic device or a protection panel of an information display unit. 2. Description of the Related Art Due to its usage, electronic devices, particularly portable electronic devices, are required to have durability that does not break when dropped from a hand or a desk. However, parts fixed with the double-sided pressure-sensitive adhesive sheet sometimes fall off when the device falls. This is considered to be due to the fact that the parts fell off because the joints could not withstand the impact generated during the fall. In particular, when fixing parts with a double-sided pressure-sensitive adhesive sheet to the part where antifouling UV curable coating is applied, there is a problem that sufficient adhesive strength cannot be obtained because the UV curable coating contains silicone oil. there were.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electronic apparatus in which a component is fixed with a double-sided pressure-sensitive adhesive sheet, and when the electronic device falls, the component is less likely to fall off due to the impact.
An object of the present invention is to provide a double-sided pressure-sensitive adhesive sheet having excellent impact resistance.

[0004]

Means for Solving the Problems The present inventors have found that the pressure-sensitive adhesive layer on at least one side of the double-sided pressure-sensitive adhesive sheet has a maximum loss tangent in a frequency band higher than the maximum natural frequency generated when the electronic device is dropped. The present inventors have found that a double-sided pressure-sensitive adhesive sheet having a maximum value of the loss tangent and having a value of 1 or more exhibits high impact resistance, and solved the above-mentioned problem. That is, the double-sided pressure-sensitive adhesive sheet of the present invention, the pressure-sensitive adhesive layer on at least one side of the double-sided pressure-sensitive adhesive sheet, has a maximum value of loss tangent in a frequency band equal to or higher than the maximum natural frequency generated when the electronic device is dropped, And by setting the maximum value of the loss tangent to 1 or more, the adhesive layer of the double-sided pressure-sensitive adhesive sheet efficiently absorbs vibration energy when the electronic device falls, and the ultraviolet-curable coating surface containing the silicone oil is absorbed by the pressure-sensitive adhesive layer. On the other hand, even when the components are fixed, high tack / adhesive performance that cannot be achieved by the conventional double-sided pressure-sensitive adhesive sheet is exhibited.

In general, when a structure in which components are fixed with a double-sided pressure-sensitive adhesive sheet falls, the structure vibrates in a frequency range specific to the shape due to the impact. This is called a natural frequency region. Energy in this frequency range (vibration energy) is transmitted to the parts joined to the structure via the double-sided adhesive sheet. Therefore, as the vibration energy absorption of the double-sided pressure-sensitive adhesive sheet is higher, the vibration energy transmitted to the component is smaller, and the component is less likely to fall off. The energy absorption here refers to the ratio of converting mechanical energy into heat energy. The higher the viscosity ratio of the adhesive layer (viscoelastic body), which has both viscous and elastic properties, the higher the energy It will be excellent in absorbency.
When the elasticity (storage elastic modulus) and the viscosity (loss elastic modulus) of the pressure-sensitive adhesive layer, that is, the viscoelastic body, are measured for each frequency, the higher the frequency, the higher both values. This means that the higher the frequency, the stronger the properties of the elastic body appear.

On the other hand, the loss tangent, which is a value obtained by dividing the viscosity by the elasticity, increases as the frequency becomes higher, reaches a local maximum at a certain point, and then decreases again. On the frequency side lower than the maximum value, it exhibits behavior as a viscoelastic body (adhesive) in which viscosity and elasticity coexist, and on the frequency side higher than the maximum value, it behaves as a glassy solid. Therefore, the vibration energy in the high frequency range cannot be absorbed by the frequency having the maximum value. On the other hand, when the maximum value exceeds 1, the viscosity exceeds the elasticity and the energy absorption becomes large. From the above, if there is a local maximum value of loss tangent of the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet fixing the component in the natural frequency region generated by the impact when the structure falls, the frequency region exceeding the local maximum value The vibration energy cannot reach the component without being absorbed by the pressure-sensitive adhesive layer, and the component tends to fall off. Hereinafter, the present invention will be described in more detail.

The double-sided PSA sheet of the present invention may or may not use a support. The support is not particularly limited, and a known and commonly used support can be used. Specific examples include a porous support such as a nonwoven fabric, a cloth, and paper, and a plastic film such as a polyester film, a polyethylene film, a polypropylene film, and a polyvinyl chloride film. In the case of a film support, a surface corona treatment or an anchor coat treatment may be performed to improve the anchoring property with the pressure-sensitive adhesive layer. As for the thickness of the support, those having a thickness of 4 to 200 μm, which have been generally used, can be used, and those having a thickness of 10 to 100 μm are more preferable.

The pressure-sensitive adhesive layer used in the present invention has a maximum value of a loss tangent in a frequency band equal to or higher than a maximum natural frequency generated when the electronic device is dropped, and the maximum value of the loss tangent is 1 or more. belongs to. As described above, when the maximum value of the loss tangent is less than the maximum natural frequency, the vibration energy cannot be efficiently absorbed, and the component is likely to fall off due to the impact at the time of drop. The same applies to the case where the maximum value of the loss tangent is less than 1. Further, the double-sided pressure-sensitive adhesive sheet of the present invention has a frequency at which the loss tangent of the pressure-sensitive adhesive layer has a maximum value of at least 10 ^{3 in} order to obtain a sufficient impact-resistant pressure-sensitive adhesive strength on a UV-curable coated surface containing silicone oil. Hz or higher, and more preferably 10 ⁴ Hz or higher.

As the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, a known acrylic or rubber-based pressure-sensitive adhesive can be used. When the pressure-sensitive adhesive is acrylic, it is preferably an acrylic copolymer containing an acrylate having an alkyl side chain having 2 to 14 carbon atoms as a monomer component. More preferably, it is an acrylic copolymer containing an acrylate having an alkyl side chain having 8 to 14 carbon atoms and an acrylate having an alkyl side chain having 2 to 6 carbon atoms as monomer components. Further, as a monomer component, an acrylate ester or another vinyl monomer having a polar group such as a hydroxyl group, a carboxyl group, or an amino group in a side chain is added in a range of 0.01 to 3% by mass. Is preferred.

In order to increase the cohesive strength of the pressure-sensitive adhesive layer, a cross-linking agent may be added to the pressure-sensitive adhesive. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, and a chelate-based crosslinking agent. The gel fraction, which is an indicator of the degree of crosslinking,
Preferably, it is in the range of 25 to 65%. The gel fraction is a value obtained by dividing the mass of the residual gel when the adhesive layer is immersed in toluene for 24 hours by the mass before immersion, and indicating the percentage.

As the rubber-based pressure-sensitive adhesive, block copolymers such as styrene-isoprene-styrene, synthetic rubber-based pressure-sensitive adhesives such as polybutadiene and polybutylene, and natural rubber can be used. Further, when a silicone-based pressure-sensitive adhesive is used, the affinity with the silicone oil contained in the ultraviolet-curable coating film is high, so that the tackiness is improved. As the silicone-based pressure-sensitive adhesive, a peroxide crosslinking type or an addition condensation type may be used alone or as a mixture. Further, it can be used by mixing with an acrylic or rubber-based adhesive, or an adhesive in which a silicone component is pendant on the polymer main chain or side chain of the acrylic-based adhesive may be used. Various additives are added to the pressure-sensitive adhesive layer as long as the performance is not impaired as necessary.
For example, a tackifier resin, an antioxidant, an ultraviolet absorber, a filler, a pigment, a thickener, and the like may be added.

The coating solution for the pressure-sensitive adhesive layer of the present invention is prepared by dissolving the pressure-sensitive adhesive and, if necessary, other additives in an organic solvent. The organic solvent is not particularly limited as long as the above-mentioned components are dissolved, but known or common organic solvents such as ethyl acetate, toluene, xylene, methanol, and isopropyl alcohol are used alone or in combination. be able to. To form the pressure-sensitive adhesive layer on the support, a method in which the pressure-sensitive adhesive solution is directly applied to the support with a roll coater or a die coater or the like, or once the pressure-sensitive adhesive layer is formed on the separator, and then transferred to the support. Method.
The preferred thickness of the pressure-sensitive adhesive layer after drying is 30 to 300 μm.
m, preferably 50 to 200 μm.

The loss tangent of the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet according to the present invention can be measured by a frequency dispersion method using a viscoelasticity tester. The natural frequency range generated when an electronic device is dropped can be measured by fixing an ultrasonic sensor to the electronic device under test, recording the sensor output when the device falls from a height of about 5 to 10 cm with a digital oscilloscope, and using the Fourier By conversion, it can be measured as a natural frequency distribution.

Specific examples of electronic equipment suitable for fixing parts using the double-sided pressure-sensitive adhesive sheet of the present invention include a mobile phone, a portable personal computer, a portable information terminal (PDA), and the like. . When used for edging a display panel of an electronic device, for example, a liquid crystal display panel of a mobile phone, or fixing to a main body, etc., in order to enhance the light shielding property of a concealing portion by the double-sided pressure-sensitive adhesive sheet, all light transmission of the double-sided pressure-sensitive adhesive sheet is performed. The ratio is preferably set to 20% or less.

[0015]

The present invention will be specifically described below with reference to examples. Unless otherwise limited, “parts” represents “parts by mass” and “%” represents “% by mass”.

[Example] <Preparation of pressure-sensitive adhesive solution (1)> A reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel and a nitrogen gas inlet was charged with 30 parts of butyl acrylate and 67.9 of 2-ethylhexyl acrylate. Parts, 2 parts of acrylic acid, 0.1 parts of β-hydroxyethyl acrylate, and 0.2 parts of 2,2′-azobisisobutyronitrile as a polymerization initiator in 10 parts of ethyl acetate.
0 parts, and polymerized at 80 ° C. for 8 hours to obtain an acrylic copolymer solution having a mass average molecular weight of 700,000. Ethyl acetate was added to obtain a pressure-sensitive adhesive solution (1) having a nonvolatile content of 40%.

<Preparation of double-sided pressure-sensitive adhesive sheet (1)> 100 parts of the pressure-sensitive adhesive solution (1) was added to an isocyanate-based crosslinking agent (“Coronate L-45” manufactured by Nippon Polyurethane Co .; solid content: 45).
%), Stirred for 15 minutes, coated on a 75 μm-thick polyester film whose surface was treated with a release agent so that the thickness after drying would be 70 μm, and dried at 80 ° C. for 3 minutes did. The obtained pressure-sensitive adhesive sheet was weighed to 14 g / m ² ,
Mikiron 80, a 50-μm-thick nonwoven made of Miki special paper
The film was transferred onto both surfaces of No. 5 "and laminated with a roll under a pressure of 40 N / cm ² , and then aged at 40 ° C. for 2 days to obtain a double-sided pressure-sensitive adhesive sheet (1).

[Comparative Example] <Preparation of adhesive solution (2)> A reaction vessel equipped with a stirrer, a cold flow cooler, a thermometer, a dropping funnel and a nitrogen gas inlet 94.9 parts of butyl acrylate and 5 parts of acrylic acid , 0.1 part of β-hydroxyethyl acrylate and 0.2 part of 2,2′-azobisisobutyronitrile as a polymerization initiator were dissolved in 100 parts of ethyl acetate, and polymerized at 80 ° C. for 8 hours to give a mass. An acrylic copolymer solution having an average molecular weight of 700,000 was obtained. Ethyl acetate was added to obtain a pressure-sensitive adhesive solution (2) having a nonvolatile content of 40%.

<Preparation of double-sided pressure-sensitive adhesive sheet (2)> In 100 parts of the pressure-sensitive adhesive solution (2), 12 parts of a tackifier resin ("Superester A100" manufactured by Arakawa Chemical Co., Ltd.) and an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd.) "Coronate L-4
5; 45% solids ") and stirred for 15 minutes.
It was coated on a 75 μm-thick polyester film whose surface was treated with a release agent so that the thickness after drying was 70 μm, and dried at 80 ° C. for 3 minutes. The obtained adhesive sheet is
Transfer to both sides of a nonwoven fabric “Mikiron 805” with a basis weight of 14 g / m ² and a thickness of 50 μm made by Miki Tokusatsu, and roll it at 40 N / m
The laminate was laminated under a pressure of ² cm ² and then aged at 40 ° C for 2 days to obtain a double-sided PSA sheet (2). The pressure-sensitive adhesive solutions and the double-sided pressure-sensitive adhesive sheets prepared in Examples and Comparative Examples were tested by the following methods, and the results are shown in Table 1. A mobile phone “P205” manufactured by Matsushita Communication Industrial was used as the electronic device.

(1) Measuring equipment The natural frequency range generated when the portable telephone falls is determined by binding the ultrasonic sensor to the portable telephone with vinyl tape and outputting the sensor when the portable telephone falls from a height of about 5 to 10 cm. Is recorded by a digital oscilloscope, and the result is Fourier-transformed to measure a natural frequency distribution. The ultrasonic sensor is "AE-900S-" manufactured by NF Circuit Design Block.
WB (measurable frequency range is 2 × 10 ^{4 to} 5 × 10 ⁵ H
z) ", the digital oscilloscope is manufactured by Iwasaki Communication Equipment Co., Ltd.
"DS-8623" was used.

(2) Measurement of Loss Tangent of Pressure-Sensitive Adhesive Layer The double-sided pressure-sensitive adhesive sheets of Examples and Comparative Examples were superposed on each other to a thickness of 5 mm and aged at 40 ° C. for 2 days to obtain test pieces. Rheometrics viscoelasticity tester “Ares 2
A parallel plate having a diameter of 7.9 mm is attached to the “kSTD”, and a test piece is sandwiched between the kSTD and a frequency of 10 ⁻² Hz at 25 ° C.
The loss tangent up to 80 Hz was measured. Then, at 10 ° C, 0
The results of the same measurement performed at 10 ° C., −10 ° C., and −20 ° C. were converted into a temperature-speed value using software attached to “Ares 2kSTD”, and converted from 10 ⁻² Hz to 10 ⁶ H.
A loss tangent master curve in the z region was obtained. The frequency of the maximum value of the loss tangent was read from the master curve.

(3) Drop impact test At 23 ° C., an acrylic protective plate, which is a genuine component of the company, was attached to the liquid crystal display of a portable telephone “P205” manufactured by Matsushita Communication Industrial Co., Ltd. It was adhesively fixed with a sheet. After standing at 23 ° C. for 1 hour, the mobile phone was dropped from a height of 1.5 m onto the concrete floor, and the number of times the acrylic protective plate was dropped was counted.

(4) Adhesive strength A sample in which one side of a double-sided pressure-sensitive adhesive sheet having a width of 20 mm was lined with a 25 μm polyester film was adhered to an ABS plate coated with an ultraviolet curable coating at 23 ° C.
Reciprocating pressure was applied. After standing at -30 ° C for 1 hour, 180
It was pulled at a speed of 300 mm / min in the ° direction, and the adhesive strength (N / 20 mm) was measured.

[0024]

[Table 1]

[0025]

As is clear from the results shown in Table 1, when an electronic device having components fixed using the double-sided pressure-sensitive adhesive sheet of the present invention falls, the double-sided pressure-sensitive adhesive sheet is subjected to an impact when the electronic device falls. Having a maximum value of the loss tangent in a frequency band equal to or higher than the maximum natural frequency to be generated, and having a pressure-sensitive adhesive layer in which the maximum value of the loss tangent is 1 or more, efficiently absorbs vibration energy, Parts are hard to fall off. The adhesive strength at -30 ° C is also high. In particular, when the double-sided pressure-sensitive adhesive sheet of the present invention is used to attach a part to the surface of an ultraviolet-curable coating film containing silicone oil, the effect of the present invention is remarkably exhibited.

Continuation of the front page F term (reference) 4J004 AA04 AA05 AA10 AA11 AB01 CA02 CA04 CA05 CA06 CC02 CE01 DB02 EA05 FA05 FA08 5K067 AA33 BB04 KK17

Claims (3)

[Claims] 1. A double-sided pressure-sensitive adhesive sheet for fixing parts of an electronic device, wherein the pressure-sensitive adhesive layer on at least one side of the double-sided pressure-sensitive adhesive sheet has a frequency band equal to or higher than a maximum natural frequency generated when the electronic device is dropped. A double-sided pressure-sensitive adhesive sheet having a maximum value of a loss tangent and having a maximum value of 1 or more. 2. The method according to claim 1, wherein the maximum value of the loss tangent of the pressure-sensitive adhesive layer is 1
The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive sheet has a frequency band of 0 ³ Hz or more. 3. The double-sided pressure-sensitive adhesive sheet according to claim 1, wherein the electronic device is a mobile phone.